1. Field of the Invention
The present invention relates to a charge unit, and more particularly to a contact charge unit used in electrophotographic image-forming devices such as laser printers, photocopy machines, and a facsimile machines.
2. Description of the Related Art
Typically, charge units are used for charging a photosensitive member in an electrophotographic device. The charge units can be categorized into contact and non-contact types. Contact type charge units require a lower energization voltage and generate less ozone than do non-contact types.
Japanese Laid-Open Patent Publication (Kokai) No. HEI-2-282280 discloses a contact type charge unit as shown in FIG. 1. The charge unit includes a resiliently deformable resistor member 61 that is urged against the peripheral surface of a photosensitive drum 69 by a cantilever made from leaf spring 62. The photosensitive drum 69 is formed from an aluminum tube 68 coated with a photosensitive layer 67 on the peripheral outer surface thereof. The resistor member 61 is made from urethane rubber, acrylonitrile-butadiene rubber (NBR), or other suitable material. The leaf spring 62 is made from approximately 100 micrometer thick stainless steel whose one end is fixed to a conductive support member 63 by a screw 65. A pressing member 64 is provided so as to force the leaf spring 62 toward the photosensitive layer 67 of the drum 69 so that the resilient resistor member 61 presses against the photosensitive layer 67. A power source 66 is connected to the support member 63 by an electrical wire.
In such a conventional contact type charge unit, it has proven difficult to apply a uniform voltage to the resistor member 61. Attempts have been made to solve this problem, such as applying an AC current or providing a multi-layer resistor member, but these result in a more complex configuration.